The present invention relates to a motor actuator control system in which the number of rotations (rotational position shift amount) of a motor is detected to control the motor. The present invention is preferably applied to, for example, an air conditioning system for a vehicle in which a switching member such as a damper and an air mixing door of an air passage is driven by a motor actuator. In the air conditioning system, the position of the switching member is accurately controlled by the motor actuator control system of the present invention.
A switching member such as a damper and an air mixing door is used to switch the air flow mode between internal air circulation and exterior air introduction, to change air flow passages leading to interior air outlet ports, and to control air mixing rate between hot air and cool air in an air conditioning system for a vehicle. Those actions in response to an operation of switches close to the driver""s seat are implemented by driving the switching member using a motor actuator. To ensure that the switching member is moved to a predetermined position, the position and the position shift amount of the switching member needs to be detected, and a motor in the actuator needs to be controlled on the basis of the detected information.
A system using current surges periodically generated in the motor is proposed to detect the position and the position shift amount of the switching member. In the motor, a commutator rotated synchronously with a rotor slides on and discontinuously contacts brushes to pass an electric current to rotor coils, so the contact between the commutator and the brushes is periodically made and broken. A current surge (commutator surge) is generated at the moment that the contact is broken, so commutator current surges are periodically generated. Thus, the number of rotations of the motor (rotational position shift amount) is detected by counting the commutator current surges, and the position shift amount of the switching member can be determined based on the number of the surges.
The commutator current surges are generated a plurality of times per one rotation of the rotor, so the detection based on commutator current surge count is basically accurate. However, the commutator current surges are so weak when the motor starts and stops rotating that weak commutator current surges are not always detected. In addition, the commutator current is generated only while the motor is electrically powered, so the commutator current surge count becomes inaccurate if the rotor rotates by its own momentum or is rotated by unexpected force after the motor is switched off. Therefore, the detection based on the commutator current surge count is not reliable enough.
The present invention has been made in view of the above aspects with an object to provide a motor actuator control system in which the number of rotations (rotational position shift amount) of a motor is accurately controlled by correlating a count of commutator surge current and a predetermined rotational position of a gear in a gear train connected to the motor.
In the present invention, the motor actuator control system includes a motor actuator having a motor, an output shaft for outputting rotational motion of the motor at reduced rotational speed, and a gear train constituted of a plurality of gears to transmit rotational motion of the motor to the output shaft while reducing rotational speed. The control system further includes a first detector detecting commutator current surges, a second detector detecting a predetermined rotational position of a gear, and a control unit controlling the motor on the basis of a signal from the first detector and another signal from the second detector.
The commutator current surges are counted by the control unit. When the second detector detects the predetermined position of the output gear which is connected to the output shaft and rotated at the slowest speed in the gear train, the count of the commutator current surges is correlated with the predetermined rotational position by substituting a predetermined number for the count. Then, the motor is driven until the count reaches another predetermined number in order to rotate the output shaft to another predetermined rotational position.